JP3438465B2 - Magnetic iron oxide particles, magnetic iron oxide particle powder for magnetic toner mainly comprising the particles, method for producing the same, and magnetic toner using the magnetic iron oxide particle powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner for a magnetic toner capable of obtaining a high-resolution image in electrostatic latent image development because it does not fall off from toner particles and has good fluidity when made into a toner. The present invention relates to iron oxide particle powder, a method for producing the same, and a magnetic toner using the magnetic iron oxide particle powder.

[0002]

2. Description of the Related Art As one of electrostatic latent image developing methods, a so-called "developing agent" which uses composite particles obtained by mixing and dispersing magnetic particle powder such as magnetite particle powder in a binder resin without using a carrier. The developing method using "one-component magnetic toner" is widely known and widely used.

In recent years, as electrostatic copying machines and printing machines have become smaller and faster, and the performance has been improved, the characteristics of magnetic toner as a developer have been improved, that is, stable developing performance has been obtained even under hard conditions. There is a strong demand for a magnetic toner having excellent durability. Further, there is a demand for a magnetic toner that can obtain high resolution due to its high fluidity.

Usually, the magnetic toner is composed of magnetic particles and a binder resin, and the magnetic particles are uniformly dispersed in the toner particles. The magnetic particles exposed on the surface of the toner particles are easily separated from the toner particles due to friction or the like, and in particular, in a small particle size toner, the ratio of the magnetic particles exposed on the surface is large, and the magnetic particles separated from the surface of the toner particles are small. Problems have arisen such that not only the environment of the equipment is deteriorated due to pulverization but also the uniform charging of the toner is hindered, but also the magnetic particle powder that has fallen off is scattered during electrostatic development, and the developability is deteriorated.
Therefore, there is a strong demand for magnetic particle powders that have excellent durability and that do not fall off even when exposed to the surface of toner particles.

The resolution at the time of developing an electrostatic latent image is described in JP-A-63-139367, "In order to form a visible image of good image quality in the method using such a dry developer, It is necessary that the developer has high fluidity and uniform chargeability, and the fluidity and uniform chargeability of the toner particles, which are the developer, are greatly involved as described in "...". . Therefore, in order to obtain a high-resolution image, a toner having a high fluidity and a uniform charging property is required.

The various characteristics of the magnetic toner and the various characteristics of the magnetic particle powder mixed and dispersed in the magnetic toner are closely related to each other, and the fluidity of the magnetic toner depends on the fluidity of the magnetic particles exposed on the surface of the magnetic toner particles. It depends largely on the surface condition. Therefore, JP-A-5-72801 and JP-A-5-2136 are used.
It is known that the use of magnetic particle powder having Si on the surface is effective for improving the fluidity of the magnetic toner, as described in JP-A No. 20 and JP-A No. 7-101731.

Magnetite particle powders used as magnetic particle powders for magnetic toners include octahedral magnetite particle powders (Japanese Patent Publication No. 44-668) and spherical magnetite particles (Japanese Patent Publication No. 62-51208). In addition, magnetite particles having a hexahedron (Japanese Patent Laid-Open No. 3-201109) are known.

As a characteristic particle shape, magnetite particles having granular projections on the particle surface (Japanese Patent Laid-Open No. 345616/1993), the number of surfaces is at least 1.
Magnetite particles having 0 or more polyhedrons (Patent Document 5)
No. 43253).

[0009] Conventionally, in order to improve the characteristics of magnetite particles, a manufacturing method in which Si is added during a magnetite-forming reaction has been studied. For example, a silicon component is added to a ferrous salt solution to add iron to iron. After mixing with 1.0 to 1.1 equivalents of alkali, the pH is maintained at 7 to 10 to carry out the oxidation reaction, and 0.9 to 1.2 relative to the initial alkali during the reaction.
A method of obtaining magnetite particles by adding an equivalent amount of insufficient iron and carrying out an oxidation reaction while maintaining the pH at 6 to 10 (Japanese Patent Laid-Open No. 213620/1993), and Fe ²⁺ of 0.
In producing magnetite particles by passing an oxygen-containing gas through a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid obtained by reacting 80 to 0.99 equivalents of alkali hydroxide, water-soluble silica is used. Acid salt to Fe to S
A method of obtaining spherical magnetite particle powder by adding 0.1 to 5.0 atom% in terms of i and performing two-step reaction (Japanese Patent Publication No. 3-9045), equivalent to or more than ferrous salt solution Is added to the hydroxosilicate solution during the oxidation reaction to magnetite particles after the production of ferrous hydroxide, the Fe ²⁺ / Fe ³⁺ ratio in the reaction solution is 10 to 1.0.
At a certain time, there is a method for producing a magnetite pigment (Japanese Patent Publication No. 1-36864) which is added at a ratio of 0.5 to 3.0% by weight in terms of Si / Fe ₃ O ₄ .

[0010]

Since the toner particles do not fall off, the fluidity of the toner is good, and the uniform charging property is obtained, a high resolution image quality is obtained in electrostatic latent image development. The magnetic iron oxide particle powder for magnetic toner to be obtained is currently most demanded, but such magnetic iron oxide particle powder for magnetic toner has not been provided yet.

That is, the magnetite particle powder described in the above-mentioned Japanese Patent Laid-Open No. 5-345616 has granular projections on the particle surface, but the individual projections are fine, and sufficient dropout prevention is possible. It is less effective.

The magnetite particle powder described in JP-A-5-43253 is composed of particles having 10 or more faces, but has no unevenness and therefore has no effect of preventing falling off from the toner surface. Is.

The magnetite particles described in JP-A-5-213620 mentioned above are obtained by adding 1.0 to 1.1 equivalents of alkali to ferrous iron in the primary reaction, and the obtained magnetite particles are Since it is close to a sphere, it cannot be obtained with a large particle size distribution and a uniform particle size.

The magnetite particles described in Japanese Patent Publication No. 3-9045 have no pH adjustment during the primary reaction, have a pH as low as less than 8.0, and have a spherical shape.

The magnetite particles described in the above Japanese Patent Publication No. 1-36864 have an octahedral shape and do not have irregularities and therefore have no effect of preventing the toner particles from falling off. .

Therefore, according to the present invention, the toner particles do not fall off, the fluidity of the toner is good, and the uniform charging property is obtained. Therefore, a high resolution image quality is obtained in the electrostatic latent image development. It is a technical object to provide a magnetic iron oxide particle powder for a magnetic toner and the magnetic iron oxide particle powder obtained.

[0017]

The above technical problems can be achieved by the present invention as follows.

That is, in the present invention, the particle size is 0.05 to 0.
50 μm, which is 0.9 to 6 with respect to Fe in terms of Si.
Magnetite particles containing 5 atomic% of silicon, the particle shape of which is round-cornered sugar-based sugar particles based on a granular shape, and the number of convex protrusions on the particle surface on the projected view is 2 to 30. The magnetic iron oxide particles are characterized by being in the range.

Further, the present invention has an average particle size of 0.05 to
0.50 μm, which is 0.9 to Fe with respect to Si.
A magnetic iron oxide particle powder for a magnetic toner, wherein the magnetic iron oxide particles are contained in an amount of 60% or more in a magnetite particle powder containing 6.5 atomic% of silicon.

Further, the present invention was obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali hydroxide in an amount of 0.80 to 0.99 equivalent to the ferrous salt in the aqueous solution of ferrous salt. 70 to 10 in a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid
A first-step reaction in which an oxygen-containing gas is aerated to generate magnetite seed crystal particles while being heated to a temperature range of 0 ° C., and 1.00 equivalent or more of water relative to residual Fe ²⁺ after completion of the first-step reaction Manufacture of magnetite particle powder comprising a two-step reaction of adding an alkali oxide aqueous solution and aeration of an oxygen-containing gas while heating in the temperature range of 70 to 100 ° C. to cause a growth reaction of the magnetite seed crystal particles. In law,
During the first-step reaction, 1.0 to 8.
0 atom% of water-soluble silicate aqueous solution is added at least twice in a divided manner, or is added dropwise at a rate of 0.5 to 5.0% per minute with respect to the total amount of Si added, A magnetic toner having a pH in the range of 7.5 to 9.5 when the degree of oxidation of Fe ²⁺ (Fe ³⁺ / total Fe) in the first-step reaction is 20% or more. It is a method for producing magnetic iron oxide particle powder for use.

Further, the present invention is a magnetic toner using the above magnetic iron oxide particle powder for magnetic toner.

The structure of the present invention will be described in more detail as follows. First, the magnetic iron oxide particles according to the present invention will be described.

The magnetic iron oxide particles according to the present invention are compositionally composed of magnetite particles (( FeO ) x.Fe ₂ O ₃ , 0 <
x ≦ 1).

The magnetic iron oxide particles according to the present invention have a particle size of 0.05 to 0.50 μm, preferably 0.10 to 0.3.
It is 0 μm.

The magnetic iron oxide particles according to the present invention are particles having a round shape and rounded corners, and are in the form of syrup-like sugar particles, and have 2 to 30 convex protrusions, preferably 5 protrusions on the surface of the particles on the projection view. ~
It has 20 pieces. When the particle shape is a well-known spherical shape, an octahedron, a hexahedron, a polyhedron, etc., the particles easily fall off when they are exposed on the surface of the toner particles. When the number of the protrusions is less than 2, the effect of preventing the toner particles from falling off from the surface becomes small. When the number of particles exceeds 30, the number of contact portions with the resin on the surface of the toner particles increases, but the individual projections become small, and sufficient effect of preventing falling cannot be obtained.

The convex protrusion in the present invention satisfies the following conditions. That is, on the projected view of the magnetic iron oxide particles (transmission electron micrograph, etc.), (1) Both ends of the protrusion are concave. (2) If two or more protrusions overlap each other, only the tip of the protrusions should be protrusions. (3) The length (a) and height (b) of the bottom of the protrusion and the particle diameter (c) of the particles should satisfy the following formulas. i) 10 ≦ a / c × 100 ≦ 40 ii) 5 ≦ b / c × 100 ≦ 30

The above items (1) and (2) are visually determined on the projection view (transmission electron micrograph, etc.). Regarding the above (3), the length (a) of the bottom side of each of the protrusions on the particle surface of the magnetic iron oxide particles in the above projection diagram (transmission electron micrograph etc.),
The height (b) and the particle diameter (c) of the particles are measured to calculate a / c and b / c, and the conditions i) and ii) are calculated.
It is determined whether or not

FIG. 1 is a conceptual explanatory view in which the morphology of the magnetic iron oxide particles satisfying the conditions (1) to (3) is enlarged and schematically shown. “Both concave” means the portion indicated by arrow A, “only the tip end portion” in (2) above indicates the portion indicated by arrow B, and “length (a), height (in the above (3)) "b) and particle diameter (c)" are a, b and c in the figure.

Next, the magnetic iron oxide particle powder for magnetic toner according to the present invention will be described.

The magnetic iron oxide particle powder for magnetic toner according to the present invention is composed of magnetite particles (( FeO ) x.
Fe ₂ O ₃ , 0 <x ≦ 1), and as shown in the electron micrograph of FIG. 2 to be described later, it is in the form of rounded-cornered sugar based on granules, and convex projections are formed on the surface of the particles. 2-30
It is a particle powder containing 60% or more, preferably 70% or more, of the number of the magnetic iron oxide particles to be contained. If the number ratio is less than 60%, the effect of preventing the toner particles from falling off from the surface of the toner particles becomes small when the toner is used. Here, the convex protrusion means one that satisfies the above conditions (1) to (3).

The number ratio was calculated as a percentage of the total number of particles measured by measuring the number of magnetic iron oxide particles satisfying the conditions (1) to (3) in a transmission electron micrograph. The total number of particles measured at this time is 30 or more, preferably 50 or more.

The magnetic toner magnetic iron oxide particle powder according to the present invention has an average particle diameter of 0.05 to 0.50 μm, preferably 0.10 to 0.30 μm. Average particle size 0.0
When the particle size is less than 5 μm, the number of particles in the unit volume becomes too large, and the number of contact points between particles increases, so that the adhesive force between the powder layers increases, and when the magnetic toner is used, the amount of particles in the binder resin increases. Dispersibility deteriorates. If it exceeds 0.50 μm,
The number of magnetic iron oxide particles contained in one toner particle decreases, and the distribution of the magnetic iron oxide particles in each toner particle becomes uneven, resulting in impaired uniformity of toner charging.

The magnetic toner for magnetic iron oxide particles according to the present invention, BET specific surface area of 3~30m ² / g, preferably from 5 to 20 m ² / g.

The magnetic iron oxide particle powder for magnetic toner according to the present invention has a saturation magnetization value of 80 to 92 Am ² / kg , preferably 82 to 90 Am ² / kg . 92 Am ²
The value of / kg is the theoretical value of magnetite, and it does not exceed this value. If it is less than 80 Am ² / kg , the amount of Fe ^{2+ in} the particles decreases, and it becomes reddish, which is not preferable as the magnetic iron oxide particle powder for magnetic toner.

The magnetic iron oxide particle powder for magnetic toner according to the present invention has an Fe ²⁺ content of 12 to 24% by weight, preferably 17 to 24% by weight, based on the total weight of the magnetic iron oxide particles. If it is less than 12% by weight, sufficient blackness cannot be obtained. When it exceeds 24% by weight, it is easily oxidized and becomes environmentally unstable.

The magnetic iron oxide particle powder for a magnetic toner according to the present invention contains Si in an amount of 0.9 to 6.5 atom%, preferably 1.3 to 5.3 atom% with respect to Fe. When the Si content is less than 0.9 atomic%, the Si contained on the surface
As a result, the liquidity becomes poor. When the content is 6.5 atomic% or more, the amount of silicon contained increases, so that the hygroscopicity becomes high, which may affect the environmental stability of the toner when used as a toner. In addition, Si that is present separately from the magnetic iron oxide particle powder may hinder the uniform charging and deteriorate the charging stability. The Si content on the surface of the particles is 0.05 to 1.
It is 0 atom%, preferably 0.08 to 0.80 atom%. If it is less than 0.05 atom%, good fluidity cannot be obtained when the toner is used. When it exceeds 1.0 atom%, the hygroscopicity becomes high, and when it is used as a toner, it may affect the environmental stability of the toner.

The magnetic iron oxide particle powder for a magnetic toner according to the present invention has a good fluidity because the degree of compression, which is an index of fluidity, is 50 or less, preferably 45 or less.

The magnetic iron oxide particle powder for magnetic toner according to the present invention has a charge amount of 0 to -60 μC / g, preferably -2.
˜−50 μC / g.

Next, a method for producing the magnetic iron oxide particle powder for magnetic toner according to the present invention will be described.

Examples of the ferrous salt aqueous solution in the first-step reaction of the present invention include ferrous sulfate aqueous solution and ferrous chloride aqueous solution.

Examples of the aqueous alkali hydroxide solution in the first-step reaction of the present invention include aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth metal solutions such as magnesium hydroxide and calcium hydroxide. An aqueous solution of a hydroxide, an aqueous solution of an alkali carbonate such as sodium carbonate, potassium carbonate or ammonium carbonate, and aqueous ammonia can be used.

The amount of the alkali hydroxide aqueous solution used before the pH adjustment in the first-step reaction is 0.80 to 0.99 equivalent to Fe ²⁺ in the ferrous salt aqueous solution. The range is preferably 0.90 to 0.99 equivalents. When the amount is less than 0.80 equivalent, goethite is mixed in the product, and the target magnetite particles cannot be obtained as a single phase. When it exceeds 0.99 equivalents, the particle size distribution becomes large, and particles having a uniform particle size cannot be obtained.

The reaction temperature in the first stage reaction of the present invention is 7
It is 0 to 100 ° C. If the temperature is lower than 70 ° C., acicular goethite particles are mixed. Magnetite particles are also produced when the temperature exceeds 100 ° C., but this is not industrially easy because an apparatus such as an autoclave is required.

The oxidizing means in the first-step reaction of the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid.

As the water-soluble silicate used in the first-step reaction of the present invention, sodium silicate, potassium silicate and the like can be used. The amount of the water-soluble silicate added is 1.0 to 8.0 atom%, preferably 1.5 to 6.5 atom% in terms of Si with respect to Fe. If it is less than 1.0 atom%, the particles become hexahedral particles, and the effect of preventing the particles from falling off from the toner surface becomes poor. On the other hand, when it exceeds 8.0 atomic%, needle-shaped goethite particles are mixed.
Further, since the amount of silicon contained increases, the amount of adsorbed water increases, which may affect the environmental stability of the toner when used as a toner. In addition, Si that is precipitated separately from the magnetic iron oxide particle powder hinders uniform charging, resulting in poor charging stability.

The water-soluble silicate should be added in the first-step reaction by oxygen-containing gas being passed through the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid during the first-step reaction. It is necessary to be in the process of generating magnetite nucleation particles. The addition method can be carried out by dividing the mixture into two or more times, preferably five or more times, or by continuously dropping. The dropping rate in the case of continuous dropping is 0.5 to 5.0% per minute, preferably 1.0 to 3.0% per minute, based on the total amount of the water-soluble silicate added.
Is. In the case of adding all at once, it is not preferable because Si is not easily contained in the magnetic iron oxide particles to be produced, and Si is precipitated alone.

In the first stage reaction of the present invention, ferrous iron F
In oxidation degree (Fe ³⁺ / whole Fe) in the range of 20% or more of e ^2+, range of pH of the suspension is 7.5 to 9.5, further, the degree of oxidation (Fe ³⁺ / whole When Fe) is 30% or more, the pH of the suspension is set to be 8.0 to 9.5. When the pH of the suspension is not within this range, the pH of the suspension is adjusted to the range of 7.5 to 9.5 with an acid such as sulfuric acid or an alkali such as an aqueous solution of alkali hydroxide. Suspension pH
When the value is less than 7.5, the surface of the particle has less irregularities, and the particle has a nearly spherical shape, and the effect of preventing the toner from falling off from the surface is not sufficient. If the suspension pH exceeds 9.5, it becomes difficult for Si to be contained on the particle surface,
When it is used as a toner, it has poor fluidity.

The amount of the aqueous alkali hydroxide solution used in the second-step reaction of the present invention is 1.00 equivalent or more with respect to the Fe ²⁺ remaining at the start of the second-step reaction. 1.0
If the amount is less than 0 equivalent, all the remaining Fe ²⁺ will not precipitate. Practically, an amount of 1.00 equivalent or more considering industrial properties is preferable.

The reaction temperature in the second-step reaction of the present invention can be selected from the same conditions as in the first-step reaction. The oxidizing means can be selected from the same conditions as in the first-step reaction.

It should be noted that, after the addition of the raw materials and between the first-step reaction and between the first-step reaction and the second-step reaction, sufficient agitation may be carried out for a required time if necessary.

The magnetic toner according to the present invention will be described.

The magnetic toner according to the present invention has a volume average particle diameter of 3 to 20 μm, preferably 5 to 15 μm.

The magnetic toner according to the present invention comprises the above magnetic iron oxide particle powder for magnetic toner and a binder resin, and optionally contains a releasing agent, a coloring agent, a charge control agent, and other additives. You may. The ratio of the binder resin to the magnetic iron oxide particle powder for magnetic toner is 20 to 150 parts by weight, preferably 30 to 120 parts by weight, relative to 100 parts by weight of the binder resin. .

The magnetic toner according to the present invention is such that the magnetic iron oxide particles hardly fall off from the toner surface.

The magnetic toner according to the present invention has high fluidity and thus can obtain high resolution image quality.

As the binder resin used in the magnetic toner, a vinyl polymer obtained by polymerizing or copolymerizing vinyl monomers such as styrene, alkyl acrylate and alkyl methacrylate can be used. As monomer styrene constituting the binder resin, for example, styrene,
There are styrenes such as α-methylstyrene and p-chlorostyrene and substitution products thereof, and examples of alkyl acrylates include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate,
There are octyl acrylate, isobutyl acrylate and hexyl acrylate, and as the methacrylic acid alkyl ester, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, isobutyl methacrylate, dodecyl methacrylate,
There are monocarboxylic acids having a double bond such as hexyl methacrylate and substituted products thereof. The copolymer preferably contains 50 to 95% by weight of a styrene component.

For the production of the above-mentioned copolymer, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization are used. In addition to these components, a known polymer or copolymer such as polyester resin, epoxy resin, polyurethane resin, etc. can be used as the binder resin, if necessary.

In preparing the magnetic toner, 20 to 150 parts by weight, preferably 30 to 120 parts by weight of the magnetic iron oxide powder for magnetic toner according to the present invention is used with respect to 100 parts by weight of the binder resin. Is good.

As the releasing agent, paraffins having 8 or more carbon atoms, polyolefins and the like are preferable, and for example, polyethylene, polypropylene, paraffin wax, paraffin latex, microcrystalline wax, carnauba wax and the like can be used. In general, the blending amount of these polyolefins is preferably in the range of 1 to 10% by weight.

As the colorant, any suitable pigment or dye can be used as required. For example, carbon black, chrome yellow, aniline blue, phthalocyanine blue, ultramarine blue, quinacridone, benzidine yellow and the like can be used.

As the charge control agent, a fluorine-based surfactant, an azo metal complex salt, a salicylic acid chromium complex, a dialkyl salicylic acid, a metal complex salt of naphthoic acid, an azine dye such as nigrosine, a quaternary ammonium salt, and carbon black are used. it can.

As another additive, as an abrasive,
Tin oxide, strontium titanate, barium titanate, tungsten carbide and the like can be used, and even if resin fine particles or inorganic fine particles that act as a charging aid, a conductivity-imparting agent, an anti-caking agent, a fluidity-imparting agent are added. Good.

The magnetic toner according to the present invention can be prepared by a known method such as mixing, kneading and pulverizing. Specifically, the magnetic iron oxide particle powder for magnetic toner and the binder resin are used. If necessary, a colorant, a release agent, a charge control agent, other additives, etc. are first thoroughly mixed by a mixer, and then a resin or the like is melted and kneaded by a heating kneader to be compatibilized. After magnetic iron oxide particles and the like are dispersed and solidified by cooling, the obtained resin kneaded product is pulverized and classified to obtain a magnetic toner.

As the mixer, a Henschel mixer, a ball mill or the like can be used.
As the heating and kneading machine, a heating and kneading machine such as a roll mill, a kneader, a twin screw type, an extruder can be used. The pulverization can be performed by a pulverizer such as a cutter mill or a jet mill, and the classification can be performed by a known method.

As another method for obtaining the magnetic toner according to the present invention, there is a suspension polymerization method or an emulsion polymerization method. In the suspension polymerization method, a polymerizable monomer, magnetic iron oxide particle powder for magnetic toner, and coloring are used. Agent, a polymerization initiator if necessary, a cross-linking agent, a charge control agent, and a monomer composition in which other additives are dissolved or dispersed are added to an aqueous phase containing a suspension stabilizer while stirring. It can be granulated and polymerized to form toner particles.

In the emulsion polymerization method, a suitable particle size can be obtained by adding an emulsifier in the process of dispersing monomers, magnetic iron oxide particle powder for magnetic toner, colorant, polymerization initiator and the like in water to carry out polymerization. Toner particles can be formed.

[0067]

In order to suppress the pulverization due to the drop of the magnetic particle powder from the toner particle surface,
Surface treatment has been performed in order to more firmly bond the particle surfaces of the magnetic particles to the resin. However, when the present inventor considers the binding property between the particle surface and the resin, it is considered that increasing the contact area is effective in terms of preventing the toner particles from falling off from the toner surface. The present invention has been made as a result of earnestly examining whether or not a shape having unevenness can be obtained.

The present inventor, in the method for producing magnetite particle powder consisting of two-step reaction, added 1.0 to 8.0 atomic% of water-soluble silicate solution in terms of Si to Fe during the first step reaction. Add it at least twice or more,
Or, it is added dropwise at a rate in the range of 0.5 to 5.0% per minute with respect to the total amount of Si added, and the degree of oxidation of Fe ²⁺ (Fe ³⁺ / total Fe) during the first step reaction. In the range of 20% or more, pH is in the range of 7.5 to 9.5 to obtain round, rounded-corner sugar-like magnetite particles with a basic shape. When used as a toner, the particles fall off the toner surface. It is excellent in durability and has a high fluidity when used as a toner because it contains Si on the surface of particles, and uniform chargeability is obtained, so that high-resolution image quality is obtained in electrostatic latent image development. It was found that the obtained magnetic iron oxide particle powder for magnetic toner can be obtained.

[0069]

BEST MODE FOR CARRYING OUT THE INVENTION A typical embodiment of the present invention is as follows.

The average particle diameter of the magnetic iron oxide particle powder is the average value of the numerical values measured from electron micrographs, and the specific surface area is the value measured by the BET method. The magnetic properties are
"Vibration sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.) was used, and the external magnetic field was measured up to 10 KOe.

The particle shape of the magnetic iron oxide particle powder was observed with a scanning electron microscope (Hitachi S-800). Also,
Regarding the protrusions on the surface of the magnetic iron oxide particles, those satisfying the following conditions were recognized as convex protrusions. That is, a projection view of magnetic iron oxide particles (transmission electron micrograph)
In the above, (1) Both ends of the protrusion are concave. (2) If two or more protrusions overlap each other, only the tip of the protrusions should be protrusions. (3) The length (a) and height (b) of the bottom of the protrusion and the particle diameter (c) of the particles satisfy the following formulas. i) 10 ≦ a / c × 100 ≦ 40 ii) 5 ≦ b / c × 100 ≦ 30

The above items (1) and (2) are visually determined on the projection diagram (transmission electron micrograph). As for the above (3), the length (a) of the base and the height (b) of the projections on the particle surface of the magnetic iron oxide particles in the projection view (transmission electron micrograph) and the particle Regarding particle size (c), digitizer (HP-85B (manufactured by Hewlett-Packard))
And calculate a / c and b / c according to the condition i)
And ii).

Whether or not the magnetic iron oxide particles according to the present invention are the presence or absence of the convex projections satisfying the above-mentioned conditions (1) to (3) on the particle surface in the range of 2 to 30 in the projected view. For the magnetic toner according to the present invention, the ratio of the number of particles having the number of convex protrusions on the particle surface in the range of 2 to 30 to the total number of particles is calculated. It was determined whether the powder was magnetic iron oxide particles.

The amount of Si of the magnetic iron oxide particles is a value measured by using a "fluorescent X-ray analyzer 3063M type" (manufactured by Rigaku Denki Kogyo Co., Ltd.) in accordance with "General rules for fluorescent X-ray analysis" of JIS K0119. Indicated. The amount of Si on the particle surface was measured by the following method. That is, the magnetic iron oxide particle powder and ion-exchanged water are mixed, and then dispersed and made into a suspension, which is then mixed with an aqueous alkali hydroxide solution and stirred for 30 minutes or more, and then the suspension is filtered and dried. The amount of Si of the magnetic iron oxide particle powder thus obtained was measured, and the difference from the total amount of Si before the treatment with alkali was taken as the amount of Si on the particle surface.

The Fe ²⁺ content is shown by the value obtained by the following chemical analysis method. That is, in an inert gas atmosphere, 25 cc of a mixed solution containing phosphoric acid and sulfuric acid in a ratio of 2: 1 is added to 0.5 g of magnetic iron oxide particle powder to dissolve the magnetic iron oxide particles. After adding a few drops of diphenylamine sulfonic acid as an indicator to the diluted solution of the dissolved aqueous solution, redox titration was performed using an aqueous potassium dichromate solution. The time point when the diluted solution had a purple color was taken as the end point, and the value was calculated from the amount of the aqueous solution of potassium dichromate used until reaching the end point.

The amount of charge of the magnetic iron oxide particle powder was measured by using "Blow-off charge amount measuring device TB-200" (manufactured by Toshiba Chemical Co.), and the carrier was magnetically measured by using TFV-200 / 300 (manufactured by Powder Ztec Co., Ltd.). The concentration of the iron oxide particle powder was 5%, and the mixing time was 30 minutes.

The degree of compaction of the magnetic iron oxide particle powder is represented by a value calculated by measuring the bulk density (ρa) and tap density (ρt) and substituting these values into the following formula. Compressibility = [ (ρt−ρa) / ρt] × 100 Incidentally, the smaller the compressibility is, the more excellent the fluidity is.

The bulk density (ρa) is JIS-51.
The tap density (ρt) measured by the pigment test method of No. 01 is
20cc of 10g of magnetic iron oxide particle powder after measurement of bulk density
Using a funnel, gently fill the graduated cylinder of
Then, perform the operation of naturally dropping from a height of 25 mm 60
After repeating 0 times, the amount (cc) of the magnetic iron oxide particle powder filled therein was read from the scale of the graduated cylinder, and this value was shown by the value calculated by substituting it in the following formula. Tap density (g / cc) = 10 (g) / capacity (cc)

The following method was used to evaluate the detachability of the magnetic iron oxide particle powder from the toner particle surface.
That is, the resin kneaded material obtained by kneading the magnetic iron oxide particle powder and the styrene-acrylic resin is crushed to prepare a resin kneaded material particle powder, and the resin kneaded material particle powder is shaken for 60 minutes with a paint shaker to generate. The amount of fine powder of magnetic iron oxide particles was observed by an electron microscope and evaluated by comparison with the case of using conventional spherical magnetite particles.

[0080] The aqueous ferrous 21.0l sulfuric acid containing Fe ²⁺ 1.6mol / l, with respect to addition to the aqueous sodium hydroxide solution 20.7l of 3.1N, which is prepared in advance reactor (Fe ²⁺ Corresponding to 0.95 equivalent), pH 6.
7. After producing a ferrous salt suspension containing a ferrous hydroxide colloid at a temperature of 90 ° C., 80 l / min of air was aerated to start the first-stage reaction, and at the same time, as a silicon component. No. 3 water glass (SiO ₂ 28.8 wt%) 196.3 g
(Corresponding to 4.5 atom% in terms of Si with respect to Fe) was diluted with water to make 0.3 l, which was added dropwise at a rate of 5 ml per minute. After the dropping of the water glass solution was completed, the oxidation reaction was continued while stirring for 30 minutes to complete the first-stage reaction to obtain a ferrous suspension containing magnetite nucleus crystal particles. At this time, after the start of the oxidation reaction, the degree of oxidation of Fe ²⁺ exceeds 20%, and the pH thereafter is in the range of 7.5 to 9.5, and
After exceeding 30%, the pH was in the range of 8.0 to 9.5.

After the completion of the first-step reaction, 0.4 l of a 9N aqueous sodium hydroxide solution was added to the ferrous salt suspension containing the magnetite nucleus crystal particles to adjust the pH of the suspension to 9.5. Then, at a temperature of 90 ° C., 100 l / min of air was aerated for 30 minutes to carry out a second-stage reaction to generate magnetite particles. The produced particles are washed with water, filtered, dried, and dried by a conventional method.
Crushed.

As is clear from the transmission electron micrograph (× 50000) shown in FIG. 1, the obtained magnetite particles have a particle-like shape with rounded corners and a uniform sugar particle size. The average particle size is 0.20 μm, and the value of BET specific surface area is 10.4 m ² /
It was g.

As a result of inspecting the protrusions on the particle surface by the above-mentioned inspection methods (1) to (3) for the protrusions, the number of particles having 2 to 30 protrusions per particle is the total number of particles. To 76% by number.

As a result of fluorescent X-ray analysis, this magnetite particle powder contained 3.7 atom% of Si with respect to Fe, and the amount of Si on the particle surface was 0.19 atom%. As a result of the redox titration, the Fe ²⁺ amount was 18.
It was 4% by weight and had a sufficient blackness.
As for the magnetic characteristics, the saturation magnetization value was 88.7 Am ² / kg . From the results of measuring the degree of compression, the fluidity was excellent. The charge amount was -18.0 μC / g.

A resin kneaded material particle powder, which is a pulverized product of a resin kneaded material obtained by kneading the obtained magnetite particle powder and a styrene-acrylic resin, was prepared, and the above-mentioned evaluation method was used for the falling property of the magnetic iron oxide particle powder. As a result of the evaluation by the above, it was found that it had a sufficient fall-out prevention effect.

[0086]

EXAMPLES Next, examples and comparative examples will be given.

Examples 1-4, Comparative Examples 1-7; Example 1 Ferrous sulfate aqueous solution containing Fe ²⁺ 1.6 mol / l 21.
0 l was added to 20.7 l of 3.1N aqueous sodium hydroxide solution prepared in advance in the reactor (corresponding to 0.95 equivalent to Fe ²⁺ ), pH 6.7, temperature 90 ° C.
In (1), a ferrous salt suspension containing a ferrous hydroxide colloid was produced, and then 80 l / min of air was aerated to start the first-stage reaction, and at the same time, as a silicon component, No. 3 water glass ( SiO ₂ (28.8 wt%) 196.3 g (corresponding to 4.5 atom% in terms of Si with respect to Fe) was diluted with water to make 0.3 l, and 0.06 l was added 5 times every 10 minutes. Was divided into and added. After completion of dropping of the water glass solution, 3
The oxidation reaction was continued while stirring for 0 minutes, and the first-step reaction was terminated to obtain a ferrous iron suspension containing magnetite nucleus crystal particles.
At this time, after the start of the oxidation reaction, the degree of oxidation of Fe ²⁺ exceeds 20% and the pH after that is within the range of 7.5 to 9.5, and more than 30%, the pH after that is 8. It was in the range of 0 to 9.5.

After the completion of the first-step reaction, 0.4 l of a 9N aqueous sodium hydroxide solution was added to the ferrous salt suspension containing the magnetite nucleus crystal particles to adjust the pH of the suspension to 9.5. Then, at a temperature of 90 ° C., 100 l / min of air was aerated for 30 minutes to carry out a second-stage reaction to generate magnetite particles. The produced particles are washed with water, filtered, dried, and dried by a conventional method.
Crushed.

The obtained magnetite particles have a particle-like shape of round-cornered sugar-and-plain sugar, and have a uniform particle size, and an average particle size of 0.19 μm.
The value of m and BET specific surface area was 11.3 m ² / g.

As a result of inspecting the protrusions on the particle surface by the above-mentioned inspection methods (1) to (3) for the protrusions, the number of particles having 2 to 30 protrusions per particle is the total number of particles. Was 81% by number.

As a result of fluorescent X-ray analysis, this magnetite particle powder contained 3.7 atom% of Si with respect to Fe, and the amount of Si on the particle surface was 0.21 atom%. As a result of the redox titration, the Fe ²⁺ amount was 18.
It was 2% by weight and had a sufficient blackness.
As for the magnetic characteristics, the saturation magnetization value was 88.0 Am ² / kg . From the results of measuring the degree of compression, the fluidity was excellent. The charge amount was −20.0 μC / g.

A resin kneaded material particle powder, which is a pulverized product of a resin kneaded material obtained by kneading the obtained magnetite particle powder and a styrene-acrylic resin, was prepared, and the above-mentioned evaluation method was used for the falling property of the magnetic iron oxide particle powder. As a result of the evaluation by the above, it was found that it had a sufficient fall-out prevention effect.

Examples 2 to 3, Comparative Examples 1 to 7 Type of ferrous salt aqueous solution, concentration and amount used, type and concentration of aqueous alkali hydroxide solution, addition method and amount of water glass, Adjustment p during first-step reaction
H, magnetite particle powder was obtained in the same manner as in the embodiment or Example 1 of the present invention except that the type of the aqueous alkali hydroxide solution in the second-step reaction and the reaction temperature in the second-step reaction were variously changed. Table 1 shows the main manufacturing conditions at this time.
Table 2 shows various properties of the obtained magnetic iron oxide particle powder.

[0094]

[Table 1]

[0095]

[Table 2]

The magnetite particle powder obtained in Comparative Example 1 has a hexahedral shape as apparent from the electron micrograph (× 50000) shown in FIG. Therefore, the effect of preventing the resin kneaded product from falling off from the particle surface is not sufficient, and since the particle surface contains a small amount of Si, the fluidity is poor.

Example 4 Styrene-n-butyl acrylate copolymer 100 parts by weight (copolymerization ratio = 85: 15, Mw = 250,000, Tg = 62 ° C.) Magnetic iron oxide particle powder (of the embodiment of the present invention) 80 parts by weight Positive charge control agent 1.5 parts by weight Low molecular weight ethylene-propylene copolymer 2 parts by weight The above mixture is heat-kneaded for about 15 minutes in a two-roll mill set at 140 ° C., cooled, and then coarsely pulverized. , Pulverized. Further, by classifying the fine powder and the coarse powder, a magnetic toner having a volume average diameter of 10.4 μm was obtained.

A one-component type developer comprising the obtained magnetic toner was prepared, and the image density and fog were
In addition, when the generation of fine particles of magnetic iron oxide particles from the magnetic toner was examined by a durability test by a vibration test using a paint shaker, it was found that a conventional one-component developer composed of a magnetic toner using spherical magnetic iron oxide particle powder. The image quality was higher than that in the case of using, and the durability was good with almost no generation of fine powder.

[0099]

The magnetic iron oxide particle powder for a magnetic toner according to the present invention is a fine particle having a particle size of 0.05 to 0.50 μm, and the shape of the particle is a round-corner type sugar-based sugar granule. In addition, since 60% or more of the magnetic iron oxide particles in which the number of the convex projections on the particle surface is in the range of 2 to 30 on the projected view is contained in the toner particles, Si does not fall off from the toner particles. Magnetic iron oxide for magnetic toners, which contains a large amount on the surface of the particles, has good fluidity when made into a toner, and provides uniform chargeability, resulting in high resolution image quality in electrostatic latent image development. Most suitable as particle powder.

[Brief description of drawings]

FIG. 1 is a conceptual explanatory diagram in which a form of magnetic iron oxide particles according to the present invention is enlarged and modeled.

[Explanation of symbols]

a Length of bottom of protrusion b Height of protrusion c Particle size

FIG. 2 is an electron micrograph (× 5000) showing a particle structure of magnetite particle powder obtained in the embodiment of the present invention.
0).

FIG. 3 is an electron micrograph (× 50000) showing the particle structure of the magnetite particle powder obtained in Comparative Example 1.

FIG. 4 is an electron micrograph (× 50000) showing the particle structure of the magnetite particle powder obtained in Comparative Example 2.

5 is an electron micrograph (× 50000) showing a particle structure of magnetite particle powder obtained in Comparative Example 5. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Uchida 4-1-2, Funauri Minami, Naka-ku, Hiroshima City, Hiroshima Prefecture Toda Kogyo Co., Ltd. Creative Center (72) Inventor, Kazuo Fujioka Funauri Minami, Naka-ku, Hiroshima City, Hiroshima Prefecture 4-1, 2 Toda Kogyo Co., Ltd. Creative Center (56) Reference JP-A-6-345440 (JP, A) JP-A-5-345616 (JP, A) JP-A-9-59024 (JP, A) ) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01G 49/00-49/08 C09C 1/00-3/12 G03G 9/00-9 / 10,9 / 16 H01F 1/00- 1/375

Claims (4)

(57) [Claims] 1. A magnetite particle having a particle diameter of 0.05 to 0.50 μm and containing silicon in an amount of 0.9 to 6.5 atomic% based on Fe in terms of Si, and the particle shape is granular. A magnetic iron oxide particle which is basically in the shape of a ganpe sugar having rounded corners, and has a number of convex protrusions on the particle surface in the range of 2 to 30 on a projected view. 2. The magnetite particle powder according to claim 1, wherein the magnetite particle powder has an average particle diameter of 0.05 to 0.50 μm and contains silicon in an amount of 0.9 to 6.5 atom% based on Fe in terms of Si. A magnetic iron oxide particle powder for a magnetic toner, comprising 60% or more of magnetic iron oxide particles in a number ratio. 3. A ferrous hydroxide obtained by reacting a ferrous salt aqueous solution with a 0.80 to 0.99 equivalent alkali hydroxide aqueous solution with respect to the ferrous salt in the ferrous salt aqueous solution. A first-step reaction in which an oxygen-containing gas is aerated to generate magnetite seed crystal particles while heating a ferrous salt reaction aqueous solution containing iron colloid in a temperature range of 70 to 100 ° C., and after the completion of the first-step reaction Second stage in which 1.00 equivalent or more of an aqueous alkali hydroxide solution is added to the residual Fe ^2+, and an oxygen-containing gas is passed through while heating in a temperature range of 70 to 100 ° C. to grow the magnetite seed crystal particles. In the method for producing magnetite particle powder, which comprises a two-step reaction with a reaction, a water-soluble silicate aqueous solution of 1.0 to 8.0 atomic% in terms of Si relative to Fe is used at least twice during the first step reaction. Divided into two or added, or S i 0.5 ~ min.
The solution was added dropwise at a rate in the range of 5.0%, and the pH was adjusted to 7.5 to 9 in the range in which the oxidation degree of Fe ²⁺ (Fe ³⁺ / total Fe) in the first-step reaction was 20% or more. 5. A method for producing magnetic iron oxide particle powder for a magnetic toner, wherein the range is 5. 4. A magnetic toner using the magnetic iron oxide particle powder for a magnetic toner according to claim 2.